I've been thinking about it hard what do people find charismatic, attractive in Trump and Trumpism and I think I found an answer. I am certainly not the first—nor the last—to try at it, but here it is.
It is two fold—or three depending on how you count—, first his views on culture and such resonate with most even just slightly. His general ideas, that the system is rigged, that the American dream is getting further and further away, that crime—hear poverty here— is rampant, etc. The core of his ideas is simply engulf in a thick layer of racism, xenophobia, ableism, homophobia, classism, etc. This makes it so that even if the primary message doesn't stick, the deeper one does. Slight tangent, but I do not think that he is aware of this, neither do I think he would accept such a framing.
Secondly, his unapologetic transgression of norms and rules. Or rather not directly this, but instead how he "keeps getting away with it". How one by one the institutions of society folds under him. This is the final blow that opens the door wide open to fascism in people's head. The door first weakened by his talks about resonating cultural grievance coupled with this. And the more insidious part, and actually why fascism spreads like a disease—from host to host, from person to person, transforming one by one people into rhinoceros—is that it is a self reinforcing loop. As institutions folds more institutions fold, because the people within them see that "he keeps getting away with it", working backwards to explain why it's happening—rather then going the straightforward way of "the people at the top of those institutions were weak minded"—they see those institutions folding as proof of the leader power, strength, mandate or even divine aura. Trump assassination attempt worked in the same way for many, a proof that he has some kind of aura or mandate of Heaven as they thought to themselves "he can't keep getting away with this", similarly with the dismantling of the US rule of law and constitution.
It is in that sense very reminiscent of those people who say of something outrageously dangerous and for which people are working to get it ban: "well if it was really that dangerous it wouldn't be legal in the first place (or it wouldn't have been created)", forgetting that regulation is reactive, not proactive. In a similar way, the liberal media apparatus became reactive instead of proactive, seeking news after they were uncovered rather than do the work to get them uncovered. And it is partly how he got here, the fourth pillar of liberalism folded without a squeak as they couldn't bring themselves to be proactive and attack first when their enemy was weak.
Fascism is on the rise, it works like a disease or dominoes toppling. Once the spread as started it is hard to stop, but not impossible—then we can search for a cure. And actually, stopping the spread is already dealing with half of the problem as fascism is a self reinforcing loop, once the loop is broken any small crack will make it crumble.